Marine radar with t-v receiver display

ABSTRACT

A marine radar system for small boats, the system making use of a conventional T-V receiver for the display of the radar picture. The radar system includes an antenna adapted to periodically scan a predetermined azimuthal sector with a beam of radar pulses whose repetition rate corresponds to the horizontal line scanning rate of the receiver, and means to generate a local carrier whose frequency corresponds to that of an unoccupied channel of the receiver. Echo signals produced by targets lying within the sector are intercepted by the antenna. These echo signals together with horizontal sync signals corresponding in frequency to the repetition rate of the radar pulses, and vertical sync signals corresponding to the antenna scanning rate are applied as modulation components on the local carrier to create a composite video signal simulating a T-V signal. The composite video signal is fed to the T-V receiver to provide a presentation on the cathode-ray tube thereof, whereby the triangular sector scanned by the radar is converted into a rectangular picture in which targets close to the radar site are expanded relative to those remote therefrom.

United States Patent [191 Anderson 1 July 31, 1973 1 MARINE RADAR WITHT-V RECEIVER DISPLAY [76] Inventor: Tore N. Anderson, High Ridge Rd.,

Brookfleld Center, Conn. 06805 [22] Filed: July 20, 1971 [21] Appl. No.:164,348

[52] [1.8. CI 343/5 R, 343/6 TV [51] Int. Cl. G018 9/00 [58] Field ofSearch 343/6 TV, 5 SC, 17,

[56] References Cited UNITED STATES PATENTS 3,016,530 1/1962 Skidmore343/10 X Primary Examiner-Benjamin A. Borchelt Assistant Examiner-H. A.Birmiel Attorney-Michael Ebert et al.

[57] ABSTRACT A marine radar system for small boats, the system mak- 6/Manon Mus ing use of a conventional T-V receiver for the display of theradar picture. The radar system includes an antenna adapted toperiodically scan a predetermined azi muthal sector with a beam of radarpulses whose repetition rate corresponds to the horizontal line scanningrate of the receiver, and means to generate a local carrier whosefrequency corresponds to that of an unoccupied channel of the receiver.Echo signals produced by targets lying within the sector are interceptedby the antenna. These echo signals together with horizontal sync signalscorresponding in frequency to the repetition rate of the radar pulses,and vertical sync signals corresponding to the antenna scanning rate areapplied as modulation components on the local carrier to create acomposite video signal simulating a T-V signal. The composite videosignal is fed to the T-V receiver to provide a presentation on thecathode-ray tube thereof, whereby the triangular sector scanned by theradar is converted into a rectangular picture in which targets close tothe radar site are expanded relative to those remote therefrom.

8 Claims, 9 Drawing Figures MARINE RADAR WITH T-V RECEIVER DISPLAYBACKGROUND OF THE INVENTION This invention relates generally to radarsystems, and in particular to a pulse-echo radar system for marineapplications which makes use of a conventional television receiver as atarget display device.

Radio energy is propagated at the velocity of light. By measuring thetime it takes for radio energy to reach a target and to be reflectedback to the radar site, the range of the target may readily bedetermined. A radar system must, therefore, incorporate a timing deviceto determine the interval elapsing between the transmission of-a quantumof radio energy and the reception of its echo from the target. In pulseradar, this is achieved by transmitting discrete pulses of energy ofmicrosecond duration, at a repetition rate which is such that thereflected signals from the most distant target in the range are receivedbefore the next pulse is transmitted.

In radar, the indication of the presence, location and range of detectedtargets is generally presented on a cathode-ray tube display device. Inthe Plan Position Indicator radar system (PPI), echoes appear as brightpoints or areas on the face of the cathode tube and have the sameposition relative to the origin (tube centar) as the target objects haveto the radar site. The PPI type of radar system is, therefore, widelyused in marine applications for navigation purposes. On the screen ofthe PPI tube, there are displayed in polar coordinates, the variousships, coastlines, lighthouses and other land masses and objects lyingwithin the operating range of the system.

A PPI radar system is, however, a relatively costly instrument andrepresents an investment far beyond the means of most small boat owners.Hence while a system of this type is of great value for navigationalpurposes, most small boats lack a radar facility and run serious risksparticularly when visibility is poor.

SUMMARY OF THE INVENTION In view of the foregoing, it is the main objectof the invention to provide a low-cost radar system which incorporates astandard T-V receiver as a display device and applies to the receiver acomposite video signal that simulates a conventional T-V signal,resulting in a radar picture of the targets within the range of thesystem.

More specifically, it is an object of the invention to provide a systemof the above type including a radar antenna which periodically scans apredetermined azimuthal sector, echo signals derived from targets lyingwith said sector constituting the image component of said compositevideo signal.

A significant feature of the invention resides in the fact that thecomposite video signal applied to the T-V receiver represents targetswithin a triangular sector, whereas the picture developed on the screenof the cathode-ray tube has a rectangular configuration, whereby thetriangular sector is converted into a rectangular projection therebyexpanding the image of targets in the proximity of the radar siterelative to those remote therefrom. The resultant emphasis on close-intargets renders them more noticeable. This is of practical advantage ascompared to a conventional radar system wherein close-in targets, whichare normally of greater interest, are crowded together on the screen.

Also an object of the invention is to provide an efficient and yetinexpensive radar system for marine applications making use of astandard T-V receiver which is also capable of operating in the usualmanner to present conventional programs, so that the owner has both aT-V set and a radar facility. The system in accordance with theinvention, may be used with any commercially available T-V set.Obviously, the larger the T-V screen, the greater the radar imageproduced thereby.

Briefly stated, these objects are accomplished in a radar system havinga scanning antenna which projects a beam of radar pulses having arepetition rate corresponding to the horizontal scanning rate of astandard T-V receiver serving as the radar display device, the an tennacyclically scanning a predetermined triangular sector at a ratecorresponding to the vertical scanning rate of the receiver.

A picture generator is provided to produce a composite video signalsimulating a conventional T-V signal. The generator includes means toproduce a local carrier whose frequency corresponds to that of anunoccupied channel in the receiver, means to produce a horizontal syncsignal in accordance with the radar pulse repetition rate and means toproduce a vertical sync signal in accordance with the antenna scanningrate, the horizontal and vertical sync signals as well as the echosignal derived from the antenna, being imposed on the local carrier tocreate a composite video signal simulating a T-V signal.

The composite video signal representing targets lying within thetriangular sector, is fed to the T-V receiver to develop on thecathode-ray screen thereof, a rectangular picture in which thetriangular sector is converted into a rectangular projection, and inwhich close-in targets are expanded relative to distant targets.

OUTLINE OF THE DRAWING For a better understanding of the invention aswell as other objects and further features thereof, reference is made tothe following detailed description to be read in conjunction with theaccompanying drawing, wherein:

FIG. 1 illustrates an azimuthal. sector periodically scanned by theantenna in a radar system in accordance with the invention;

FIG. 2 shows the sector imposed on a marine chart;

FIG. 3 illustrates a typical picture produced on the screen of a T-Vreceiver when using a radar system according to the invention;

FIG. 4 schematically shows the main components of a preferred embodimentof a radar system in accordance with the invention;

FIGS. 5,6,7 and 8 are waveforms illustrative of conventional T-V signalshaving synchronization signal components; and

FIG. 9 is a block diagram of a radar system according to the invention.

DESCRIPTION OF THE INVENTION The radar system in accordance with theinvention, employs a special scanning antenna and microwave assemblyadapted to radiate a beam of periodic highfrequency pulses to cyclicallyscan a prescribed sector, and to receive echoes reflected from targetslying within the sector boundaries. The echoes are displayed on thecathode-ray screen of a standard US. television receiver. We shall,therefore, first consider the image analysis technique employed in aconventional television system.

The method employed in modern television systems for analyzing andsynthesizing visual images is known as linear scanning. As applied totransmission, this involves'exploring the image to be transmitted by anelectron beam which transverses the image area in a series of horizontallines, moving over every point in the image at a constant speed, andacting to discover the degree of brightness at each point in succession.The camera tube, which includes the scanning beam, generates asuccession of electrical impulses corresponding to the successive valuesof spots discovered by the beam.

At the television receiver, the scanning process in the cathode-raydisplay tube involves moving the electron beam therein synchronouslywith the beam of the camera tube, the brightness of the cathode-ray beambeing controlled by electrical impulses transmitted from the camera tubeto the receiver, thereby recreating the image seen by the camera tube.

The total number of lines over which the scanning beam passes from thebeginning of one complete image to the beginning of the next, is knownas the total number of lines per frame. In the United States, theestablished standard is 525 lines per frame, 30 frames being producedper second. To reduce flicker in the reproduced image, interlacing isemployed whereby the image is scanned in two groups of lines, so that 60halfframes are produced per second. Thus the standard U.S. televisionreceiver scans at a rate of 15,750 lines per second.

A single scanning line corresponds to 63.3 microseconds which at thespeed of light, is 9.5 kilometers or 5.9 miles (5.1 nautical miles)round-trip from the start to the end thereof.

The width of the image relative to the height thereof in the rectangleactively employed in reproducing the image, is known as the aspectratio. This ratio under US. television standards, is 4 to 3. Thus theheight of the screen represents a distance of 4.3 miles (3.82 nauticalmiles) and the width thereof a distance of 5.9 miles (5.1 nauticalmiles). With a typical television receiver having a band width of 3.5MHz, it becomes possible to resolve targets within 45 yards of themarine radar site.

A marine radar system in accordance with the invention, operates at atransmitter pulse repetition rate of 15,750 cycles per second, therebymatching the line scanning rate of the T-V receiver employed as adisplay device. The pulse width is approximately one-tenth of amicrosecond. In a working embodiment of the invention, using a microwavesource oscillating at a peaktransmitted power of 63.3 watts, a parabolicreflector 30 inches wide by 6 inches high, having 28 db gain and areceiver noise figure of 10 db, the following system sensitivities canbe realized:

Distance A Target Size Typical Targets Nautical Miles 5.1 miles 250 sq.meters land masses 4 miles 50 sq. meters large vessels 3 miles 16 sq.meters pleasure craft 50 ft.

2 miles 3 sq. meters smaller pleasure craft 1 mile 1 sq. meter buoys,small craft 20 mile 0.2 sq. meter bugys, small crafl 10 1,000 yards 0.01sq. meter all obstacles.

Use is preferably made of a sector-scanning antenna adapted to scan 42and then snap back to the starting point to simulate the scanning linemotion. FIG. 1 shows the sector scanning angle and it will be seen thatscanning takes place 21 left of the heading of the boat 10 in which theradar system is installed, and 21 right of the heading. Thus the regionviewed by the radar system is that within the triangular boundaries ofthe sector.

Reference is now made to FIG. 2, wherein the scanned sector is imposedon a nautical chart lying within a 3.82 by 5.1 nautical miles rectangle.These distances, as pointed out previously, represent the maximum rangeof the radar system. It will be seen that the chart constitutes a truemap projection, in that the relative dimensions of the targets orobjects appearing on the chart, and their positions with respect to eachother, are substantially free of distortion. However, it must berecognized that an observer on a boat does not see a true mappresentation, for the more distant an object is from the eyes of theobserver, the smaller it appears. To an observer on a boat, adjacenttargets seem larger than distant targets.

In a PPI radar system, the center of the circular cathode-ray displayscreen represents the site of the scanning antenna, the electron beambeing swept from the center of the tube to the periphery thereof toproduce a radial trace which is rotated in synchronism with the rotatingantenna, so that the screen presentation is a true map in polarcoordinates of the region surrounding the site.

If, instead of scanning omni-directionally, the PP] system were to scana 42 sector, then the PH screen would display a true map of the sectorscanned. But in the present invention as shown in FIG. 3, in which arectangular T-V receiver screen is employed, the scanning site which isthe ships locaion, is represented at the midpoint of the left side ofthe screen rectangle, and the vertical scan of the cathode-ray beam ismade to follow the angular position of the sector-scanning antenna.When, therefore, the beam is at the very top of the rectangular screenarea, its position reflects the radar beam at the extreme left position,and when the beam is at the very bottom of the rectangular screen area,its position reflects the radar beam at its extreme right position.

As shown in FIG. 3, the rectangular screen covers 21 to the left of theships location and 21 to the right thereof. At each angular position ofthe sector scan, which is represented on the vertical scale of thescreen, the cathode-ray beam is swept horizontally to produce ahorizontal trace during which echoes received at this angle are paintedin.

As a consequence, the presentation on the screen, while not a true mapprojection, is more in keeping with what an observer on the shipactually sees, for close-in targets appear much larger than targetssituated at the extreme of the range covered by the system. While thismodified map projection in which a triangular sector viewed by the radarsystem is converted into a rectangular area, (hereinafter called an SIRprojection) somewhat exaggerates close-in targets, this exaggeration isof practical advantage, for it affords an expanded view of targets inthe immediate vicinity of the boat, which is of greater concern to thesmallboat navigator than remote objects and land masses.

For example, if a larger freighter is but a few hundred yards from theboat carrying the radar system, this freighter will be seen in anexaggerated scale on the screen close to the radar site positionthereon, as compared, say to a large ship two miles away. Assuming adense fog in which the freighter is otherwise not visible, thisexaggerated radar presentation will provide an immediate warning to thepilot.

Referring now to FIG. 4, there is shown the major components of a radarsystem in accordance with the invention, installed on a boat or othervessel or vehicle. Use is made of a standard (U.S.) T-V receiver 11,adapted to operate on the power available on the boat or by means ofbatteries. The receiver includes a cathode-ray screen 12, whose activeimage area is rectangular.

Since the T-V receiver, in a system in accordance with the invention, isnot altered in any way, and is capable of providing the usual T-Vreception for entertainment and information, one significant advantageof the invention is that the user not only is afforded a radar facility,but he also has available a conventional T-V receiver at no extra cost.

The radar system is adapted to generate video signals having a localcarrier frequency corresponding to that of an unused channel on the T-\/receiver, so that by adjusting the T-V channel selector to receive theradar channel, a radar S/R presentation is made available for navigationpurposes, and by turning the selector to other channels, one receivesthe usual TV fare.

Mounted on a mast 13 on the boat or in the pilot house, is thecombination of a radar antenna 14, a rotating scanner l5 and a base 16,housing the microwave assemblies and electronics for the radar system.Thus all components of the radar system other than the T-V receiver, arejoined together in a compact package, thereby simplifying installation.

Antenna 14 preferably takes the form of a parabolic reflecting torus,operating in conjunction with a rotating scanner constituted by acluster of four wave guide horns. The arrangement is such that as thehorns rotate, they successively cooperate with the associated torus, andas each horn comes into play, it sweeps the radar beam across a 42 scanangle from a start point to a finish point, the next operative hornproducing an identical sweep. Thus in effect, the radar beam describes a42 sector and upon completion of the sector, immediately reverts to itsstart position to repeat the sector scan. Obviously, other known formsof sector-scanning systems may be used. Also provided is a control box17 which is located on the boat at a convenient position and isconnected to the radar system and the T-V receiver.

The synchronizing waveforms shown in FIGS. 5,6,7 and 8 are the standardforms for U.S. television. It will be appreciated, however, that theexplanation which follows is applicable to any T-V standard.

As a matter of convention, T-V screens are scanned along horizontallines from left to right, the lines progressing from top to bottom as ona printed page. One full transverse from top to bottom is designated asa field" of scanning, the number of fields per second being known as thefield frequency, and the number of lines per second as the horizontalfrequency. T-V systems employ interlaced scanning, so that the sceneduring each frame is scanned twice, the system being so synchronizedthat the lines from alternate fields fill in the space between theoriginal lines.

Thus in a radar system, in accordance with the invention, in which theradar picture is presented in a rectangular area on a T-V screen, thevery top of the screen as shown in FIG. 3, represents the antenna beamat its extreme left, i.e., 21 to the left of the boats heading, thedistance or range being measured out from the left edge of the picture.Obviously, if so desired, one could mount the T-V set on a bracket orswivel whereby it could be rotated from the normal viewing position, inwhich event, the lines from the :ships position on the screen wouldextend vertically. However, there is little ambiguity in the radarpresentation when the normal T-V screen orientation is used.

The waveform in FIG. 5 shows a composite video signal just prior to avertical blanking signal, whereas that in FIG. 6 shows the same videoinformation for the next field where a space of 0.5 H has been providedfor interlacing. The waveform in FIG. 7, which is a detail betweenpoints 77 in FIG. 6, shows the transition from vertical blanking topicture and details of the horizontal pedestal or blanking signal. Thewaveform illustrated in FIG. 8 is a detail between points 88 in FIG. 6.

By convention, the absence of signals represents the white level on thescreen, black being at the base of the horizontal sync pulse. Thus thesynchronizing pulses are blacker than black." In a radar system inaccordance with the invention, the T-V screen appears white when noradar echoes are present, whereas targets show up as black spots on thescreen.

The standard blaek-on-white T-V display can be reversed by suitableelectronic circuits so that targets in a radar display are made toappear as white spots on a dark field. Alternatively, provision may bemade to provide either type of presentation, depending on whetherdaylight or night-time viewing is desired. Night viewing on a darkscreen with white targets would provide improved viewability aboard adarkened ship, whereas a white background with dark targets thereonwould, in some respects, resemble a printed map presentation for daytimeuse.

Referring now to FIG. 9, the components of the radar system are shown inblock form, control box 17 serving to switch on the necessary voltagewhich may be an A-C supply 18 or a 12V D-C battery supply 19.

A picture generator 20 is provided which includes a radio-frequencyoscillator adapted to generate a local carrier at a frequencycorresponding to that of an unused channel on the T-V receiver 11. Inpractice, a multi-channel oscillator may be provided so that the usermay switch to a frequency which is unused in the region in which thesystem is operating. Picture generator 20 also includes a horizontaloscillator and a vertical oscillator so as to produce in effect, asynthetic T-V picture in which radar echoes can be viewed. The verticalsync circuit may be synchronized with the antenna sweep structure bymeans of a magnetic pick-up providing proper framing.

Also included is a microwave generator 21, such as a magnetron, operatedby a modulator 22 to produce radar pulses at the appropriate repetitionrate. Since this repetition rate must correspond to the linescanningrate 15,750 H,) of the T-V receiver, modula tor 22 can be triggered by atrigger generator incorporated in the picture generator, or themodulator may itself produce a horizontal trigger pulse to synchronizethe horizontal lines on the T-V receiver. Thus at the instant a radarpulse is transmitted, the electron beam proceeds to scan across thecathode-ray tube to produce indications thereon in response to echosignals and representing targets in the range corresponding to thescanning line.

In practice, one may use a microwave generator producing 60 watts peakpower at 15,750 pulses per second, the pulses having a 0.1 microsecondwidth.

The horn cluster which is energized by microwave source 21, is rotatedby a scanning motor 23, the pulse output of the horns being successivelydirected onto the parabolic torus reflector 14, serving to focus themicrowave energy into a beam. Rotation of the horn causes the projectedradar beam to scan from left to right within the prescribed sector tofollow the vertical transverse on the T-V screen.

A microwave switch 24 is built into the base of the antenna. The switchis arranged so that as one horn completes its sweep, the next horn inthe cluster comes into position and during the vertical retraceinterval, switching is carried out. In this way, the radar beam motioncorresponds to the vertical sawtooth action of the cathode-ray beam.This, of course, could also be accomplished electronically with a diodearray, or with a rotating antenna array with a suitable waveguideswitch, or even by means of an oscillating antenna assembly. It is alsonot necessary to provide a full 42 sweep as shown in FIG. 1, for anacceptable presentation can be had with a smaller scanning angle, withthe advantage of simplified antenna design and an expanded presentation.

Likewise, it may be advantageous to use submultiples of the normal linefrequency to simplify the modulator and microwave source design, usingfewer lines on the T-V screen to present the target returns. Thisreduced pulsatory rate can be designed to provide averaging of targetreturns in an optimum fashion.

The radar echoes return to and are picked up by the antenna, and througha transmit-receive device 25 (such as a gas-type TR tube duplexer),enter a microwave mixer 26. A microwave local oscillator 26 produceslocal oscillations which beat with the incoming echo signals to producean IF frequency facilitating amplification of the radar return in an IFamplifier 27. The output of IF amplifier 27 is demodulated in detector28 and is supplied to a video amplifier 29, as in a conventional radar.The echo signals in the output of amplifier 29 are then combined inpicture generator with the horizontal and vertical sync pulses toproduce a composite video signal simulating a T-V signal and containingthe desired radar information. The circuits of the elements constitutingpicture generator 20, namely, the horizontal oscillator, the verticaloscillator, the trigger generator and the T-V carrier generator, are thesame as those included in existing forms of closed circuit T-V cameras.In a T-V closed circuit camera, video signals generated by the cameraare combined with horizontal and vertical sync pulses to produce acomposite video signal which is applied to a T-V display tube to createthe desired T-V image, whereas in the present invention the output ofthe radar system is combined with these sync pulses to produce acomposite video signal simulating a T-V signal which is applied to T-Vset 11 to produce the desired radar image.

In one working embodiment of this system, the antenna was arranged toprovide a scanning beam 3 or so wide in azimuth, and 20 wide inelevation, as in a typical marine radar. This can be accomplished byvarious means. One may use a parabolic torus as the basic beam-shapingreflector, fed by a moving horn rotating at a submultiple of the framefrequency (25 to 30 cps). By having four horns and a waveguide switchsection, each horn in turn as it rotates, scans the parabolic toruscausing the reflected beam to move a total of approximately 42. As thebeam reaches the extreme, the next horn comes into position to beenergized by the wave guide switch section so the beam appears to snapback to the starting point (extreme left or right), depending on thesystem choice.

With a constantly rotating four-horn cluster as described, a sawtooth"action of the antenna beam is obtained. For 30 frames per second, arotation speed of 450 rpm is required. From this rotation, the verticalscanning pulse for the T-V set indicator is derived. In practice, a thinwall radome (plastic bowl) may be used to cover the rotating horns andto protect them from wind, rain, etc. The reflector remains stationary.

In the T-V receiver, the composite video signal from the radar system isdisplayed on the screen with azimuth plotted vertically, and distance tothe target displayed horizontally, as shown in FIG. 3. Since the T-Vindicator plots azimuth on one axis, the effect is to take thetriangular sector (FIG. 1) and as shown on a true map (FIG. 2), stretchthe presentation so that it more nearly approaches what the human eyesees looking ahead at the radar eye level.

This projection spreads out the display for targets in the proximity ofthe boat and enhances their presence, thereby obviating the crowding ofsuch targets as seen on the conventional radar screen display. In theSIR projection, distortion disappears at the screen center, sothattargets dead-ahead are shown exactly. Similarly distortiondiminishes with distance and is negligible at the far edge.

Although a distance of only 5.1 miles is covered in the simple singlescan arrangement, sensitivity time control circuits may be used tosuppress signals representing close-in targets and to display onlytargets on the second scan (10.2 to 15 miles) or just display the thirdscan (15.2 to 20.4 miles).

Picture generator 20 includes a multi-frequeney carrier oscillator andselector means to adjust said oscillator frequency to correspond to thatof any channel in the television receiver.

While there has been shown and described a preferred embodiment ofmarine radar with T-V receiver display, in accordance with theinvention, it will be appreciated that many changes and modificationsmay be made therein without, however, departing from the essentialspirit of the invention.

I claim:

1. A radar system employing a standard multichannel television receiverhaving a cathode-ray tube and means to effect electron beam scanning ata predetermined line frequency and at a predetermined verticalfrequency, said reciver having at least one unused channel, said systemincluding:

A. a radar antenna adapted to scan a predetermined azimuthal sectorhaving a generally triangular configuration at a cyclical ratecorresponding to said vertical frequency,

B. means to supply microwave pulses to said antenna at a repetition ratecorresponding to said line scanscanning frequency is 15,750 lines persecond.

ning frequency or to a submultiple thereof to produce a radar beam forscanning said sector,

C. means coupled to said antenna to derive therefrom echo signalsrepresenting reflecting targets intercepting said radar beam,

D. a picture generator including means to produce a local carrier whosefrequency corresponds to said unused channel, means to producehorizontal sync pulses corresponding to said repetition rate, means toproduce vertical sync pulses corresponding to said cyclical rate andmeans to combine said horizontal and vertical sync pulses with said echosignals and said local carrier carrier to produce a composite videosignal simulating a television signal, and

E. means to apply said composite video signal to said receiver toproduce on the screen thereof, a rectangular radar picture in whichimages of targets lying within said sector having a triangularconfiguration, which are adjacent the radar antenna that is representedat the apex of the sector, are expanded in the rectangular picturerelative to those remote therefrom.

2. A system as set forth in claim 1, wherein said line 3. A system asset forth in claim 1, wherein said radar antenna is constituted by astationary reflector and rotating horn cluster operating in conjunctionwith a switch to render the horn in the cluster successively active withrespect to said reflector.

4. A system as set forth in claim 1, wherein said azimuthal sector isabout 40.

5. A system as set forth in claim I, wherein said means to supply saidpulses is constituted by a magnetron generator operating in conjunctionwith a modulator serving to activate said generator at the specifiedrepetition rate.

6. A system as set forth in claim 1, further including means to shiftthe position of said antenna in azimuth to adjust the direction of saidsector.

7. A system as set forth in claim 1, wherein said means to derive saidecho pulses includes a local oscillator, means to beat reflectivesignals picked up by said antenna with the output of said localoscillator to produce an intermediate frequency signal, and means toamplify and detect said intermediate frequency signal to produce saidecho signals.

8. A system as set forth in claim 1, wherein said picture generatorincludes a multi-frequency carrier oscillator and selector means toadjust said oscillator frequency to correspond to that of any channel insaid television receiver.

II I l 1

1. A radar system employing a standard multi-channel television receiverhaving a cathode-ray tube and means to effect electron beam scanning ata predetermined line frequency and at a predetermined verticalfrequency, said reciver having at least one unused channel, said systemincluding: A. a radar antenna adapted to scan a predetermined azimuthalsector having a generally triangular configuration at a cyclical ratecorresponding to said vertical frequency, B. means to supply microwavepulses to said antenna at a repetition rate corresponding to said linescanning frequency or to a submultiple thereof to produce a radar beamfor scanning said sector, C. means coupled to said antenna to derivetherefrom echo signals representing reflecting targets intercepting saidradar beam, D. a picture generator including means to produce a localcarrier whose frequency corresponds to said unused channel, means toproduce horizontal sync pulses corresponding to said repetition rate,means to produce vertical sync pulses corresponding to said cyclicalrate and means to combine said horizontal and vertical sync pulses withsaid echo signals and said local carrier carrier to produce a compositevideo signal simulating a television signal, and E. means to apply saidcomposite video signal to said receiver to produce on the screenthereof, a rectangular radar picture in which images of targets lyingwithin said sector having a triangular configuration, which are adjacentthe radar antenna that is represented at the apex of the sector, areexpanded in the rectangular picture relative to those remote therefrom.2. A system as set forth in claim 1, wherein said line scanningfrequency is 15,750 lines per second.
 3. A system as set forth in claim1, wherein said radar antenna is constituted by a stationary reflectorand rotating horn cluster operating in conjunction with a switch torender the horn in the cluster successively active with respect to saidreflector.
 4. A system as set forth in claim 1, wherein said azimuthalsector is about 40*.
 5. A system as set forth in claim 1, wherein saidmeans to supply said pulses is constituted by a magnetron generatoroperating in conjunction with a modulator serving to activate saidgenerator at the specified repetition rate.
 6. A system as set forth inclaim 1, further including means to shift the position of said antennain azimuth to adjust the direction of said sector.
 7. A system as setforth in claim 1, wherein said means to derive said echo pulses includesa local oscillator, means to beat reflective signals picked up by saidantenna with the output of said local oscillator to produce anintermediate frequency signal, and means to amplify and detect saidintermediate frequency signal to produce said echo signals.
 8. A systemas set forth in claim 1, wherein said picture generator includes amulti-frequency carrier oscillator and selector means to adjust saidoscillator frequency to correspond to that of any channel in saidtelevision receiver.